Air Conditioner Troubleshooting

The air conditioner system in your car is made up of a compressor, condenser, evaporator, expansion valve or orifice tube, receiver dry or accumulator, high and low side hose, climate controller, fuse, relay and a switch plus some wiring and connectors. I have made up this guide for you as I would look at a system that was not working.

To help you know what I'm talking about throughout the following information it would be good for you to look over how the system works before we begin.

Now that you have reviewed the system, there are basically two sides, the air delivery and the refrigerant re-circulation portion of the system which includes the items mentioned above. If the air is blowing from the vents but it's not cold this is where we will start, if no air is coming out of the vents begin further down in this article.

Suggested Tools and Supplies Needed

  • Air Conditioner Recharge Kit
  • A/C gauge set
  • Leak detector
  • Test light
  • Basic tools
  • Protective Eye wear
  • Work Gloves

If any of these supplies are needed they are not to expensive and are available at Amazon or the local parts store. Begin by parking your car on level ground with the emergency brake set, engine cool, wearing safety eye wear and gloves.

Step 1

There are two methods a compressor can control the refrigerant flow, the first is clutch cycling, this clutch is located on the front of the compressor and easily seen. When the system is turned on this clutch will engage which causes the refrigerant to start flowing throughout the system.

If this clutch cycles on and the off within a short amount of time the system is simply low and needs to be recharged.

The second style of compressor is designed with an internal valve which controls the refrigerant flow, you cannot visually see if the valve working. The best place to start in both of these situations is to plug a a/c gauge set or recharge kit to check the level of refrigerant present in the system.

If you have attached the connector from the gauge set or recharge kit and the system is flat with no pressure on the low side (blue) gauge there is a leak which must be fixed. Visually inspect the system and look for oily residue which is an indication of a leak.

If the system looks okay with the engine off use a refrigerant leak detector and go over the hoses, condenser, compressor and evaporator drain tube which is located on the passenger side near the floor board on the outside of the car, when the detector starts to beep quickly the leak has been found.

This is a list of potential failures.
  • Bad compressor
  • Leaking condenser
  • Failed pressure hose
  • Evaporator leak
  • O ring seal leak 

Once these items or repaired the system must be vacuumed down and recharged to get the cold air back again.

Step 2

If the charge is okay the next place I would check is the fuse which protects the system, this fuse is located in the fuse panel or power distribution center. By using your owners manual located the fuse and check it, if it's blown replace it with a new one.

If in blows again once it's been replaced there is a short in the system, most of the time this short can be related to the compressor in which case it needs to be replaced.

Step 3

When the system is switched on an electrical signal is sent to the climate control panel and then to the a/c relay which in turn supplies power to compressor. Locate the relay in the fuse panel or power distribution center using the owners manual or read the bottom or top of the lid.

A relay is like an electronic switch that can handle the load of the system where a switch would simply burn out, relay failures are common because of this extreme load.

Once you have located the relay use a test light to check the terminals for power and ground and then replace the relay to recheck the system.

Step 4

A blend door actuator is used to control the temperature of the climate control system by moving a door inside the heater plenum which differentiates between hot and cold (heater core or evaporator). If the actuator is not functioning properly usually because the plastic gears inside the unit have stripped or are broken, it can stay either stuck in the heat or cold position or somewhere in between.

When it sticks in the cold position in the summer time there isn't a problem until winter and visa versa. Sometimes when the unit fails there will be an audible ticking noise when the ignition switch is turned on and will occur for a short time. To test the actuator operation start you car and allow it the engine to warm up to operating temperature, then move the temperature control from hot to cold. You should be able to hear the door moving inside the plenum while being able to feel the temperature change from warm to hot or hot to cool. Learn more

Also, when the blend door actuator fails you can check the low side outgoing a/c line for coldness, this also tells you the refrigerant side of the system is working properly. A good way to test if the system refrigerant side of the system is working properly is to start the engine and turn the system on fully.

Next, locate the low side tube with is the larger of the two line by the firewall and see if it's cold to the touch, you can also use an infrared hand held meter for the test.

If the engine is overheating the air conditioner will be weak or not working at all. If you have been driving for sometime and you noticed the system stops working the first thing to check it the engine temperature gauge.

It's also a good idea to use a garden hose under high pressure to flush the a/c condenser free from built up dirt and leaves, this will help the air flow and cool the heated refrigerant down which helps the system work better.

Step 5

If when you start your car and turn the system on but there is no air coming from the vent system you have a blower motor or blend door issue. If the blend door has failed you will still be able to hear the fan running but not be able to feel the air coming out of the vents. Reference the the step above for an idea on what to expect, there are three to four actuators in every climate control system.

If the blower motor is not running check the fuse in the fuse panel and replace it if necessary, if the fuse is okay then the blower motor itself might be bad in which case the blower motor power and ground need to be tested. Learn more

If the electrical tests okay, then the blower motor itself has failed which is common due to age and usage and needs to be replaced, these motor can be either under the dash or hood on the passengers side. Learn more

Installing New Blower Motor
If when the system is on and the air flow is weak but still cold, some cars are equipped with the cabin air filter which is much like an engine air filter that can plug causing restricted air flow. In this case the filter must be replaced to bring back the air volume.

Replacing Cabin Air Filter
If you need more information about what you have just read please visit our forum where thousands of questions about air conditioners have been answered by our online mechanics.


Article first published